Na+-Li+ countertransport in essential hypertension

Several studies on Na+-Li+ countertransport have reported higher rates in essential hypertensive than in normotensives, with a distribution pattern which is dependent on racial and ethnic background. However, it is not well established whether this abnormality in Na+ transport is associated with an abnormal clinical setting. In the present study we have performed a kinetic analysis of the interaction of the Na+-Li+ countertransport system with internal Na+ in erythrocytes from a sample of 72 essential hypertensives and 30 normotensive controls. A significant increase in mean values of the maximal rate of Li+-stimulated Na+ efflux (Vmax; 375.1 +/- 23.8 versus 213.7 +/- 8.5 mumol/l cells per h; mean +/- s.e.m.; Mann-Whitney test: U = 500; P less than 0.0001), as well as in the apparent affinity constant for internal Na+ (KNa; 10.03 +/- 0.08 versus 6 +/- 0.4 mmol/l cells; Mann-Whitney test: U = 718; P less than 0.0079), were observed in essential hypertensives with respect to normotensives. Using the 95% confidence interval of Vmax in normotensives as the normal range, 29 (40.3%) of the essential hypertensives exhibited values above the normal upper limit. The maximal rate (Vmax) and the internal Na+ content required for half-maximal stimulation (K50%) of Na+-K+ ATPase and outward Na+-K+ cotransport, and the rate constant of Na+ leak (KPNa) in this subset were similar to the values observed in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)